Capacitor as trigger

I have a small solar panel that is connected to a 2200 uF capacitor through a diode and charges it to 1.7V maximum. I would like to create a circuit that will use the voltage across capacitor terminals as a trigger for other events. Suppose that when the capacitor is charged to exactly 1.7V, it triggers some other element and discharges through an LED. Is it possible to build such circuit without any other voltage sources except for the solar panel?

Staff: Mentor

You could use a 1.25V voltage reference with some voltage division, and have that turn on a highside PNP transistor to let current out of the capacitor and into a load. It would be good to have a bit of hysteresis in the circuit as well, depending on how you want it to work as a switch.